1. Field
The present disclosure relates to the field of products made of tissue paper for sanitary or domestic use and more particularly targets an embossing and assembling installation for manufacturing multi-ply products.
2. Description of Related Art
In the aforementioned field, products are manufactured as rolls composed, in general, of at least two plies of tissue paper. The tissue paper is a sheet of paper having a low basis weight, between 10 and 50 g/m2, that is obtained on paper-making machines designed and controlled in order to give it properties of mechanical strength, softness and absorbency with respect to the application for which it is intended. The formed sheet is wound on a reel and stored as a semi-finished product. The machines for manufacturing this type of paper are well known. The semi-finished product is subsequently converted to rolls or into formats having dimensions suitable for their use. The converting consists of the assembly of several plies into one multi-ply sheet with or without an embossing step, with or without a knurling step, making into rolls or into formats and cutting to the commercial size. The embossing makes it possible, in particular, to increase the thickness of the sheet, by modifying its mechanical properties.
There are several methods for assembling sheets. It is possible, for example, to simply superpose several plies, so as to obtain a sheet having a higher basis weight and to connect them together mechanically, by knurling for example and/or by adhesive bonding. It is possible to emboss one or more plies before assembling according to a pattern composed of discrete or continuous protuberances, so as to give the sheet more volume and improve its softness, its ability to absorb liquids and/or its attractiveness.
In a known manner, one converting installation generally comprises one or more embossing groups, with, where appropriate, an adhesive applicator. In order to emboss one ply, an embossing group is used that comprises a rigid roller, engraved on the surface with a pattern in relief as desired, and for example a roller having a deformable coating, generally made of an elastomer. The ply to be embossed is guided between the two rollers that roll against one another. The pressure exerted by the deformable roller on the ply leads to a more or less pronounced deformation of the latter which matches the relief of the engraved roller. The embossing groups are provided with means for rotating the rollers and also for controlling their separation.
In order to produce a sheet assembled in such a way that the protuberances of the relief are positioned tip-to-tip, two plies are embossed separately, then the two plies are brought close to one another so as to make all or part of the peaks of the protuberances of the two plies coincide, after having adhesively bonded at least one part thereof. The installation for producing this type of sheet comprises two separate embossing groups positioned so that all or part of the peaks of the protuberances of the two engraved rollers come into contact through the two plies that are guided between them.
Another method of assembling plies that form one sheet is known under the name of “nested”. The protuberances of one ply are nested between those of the facing ply. To produce this assembly, the two plies are embossed separately on two separate embossing groups; one ply is detached from the engraved roller on which it has been embossed then it is applied to the other ply still pressing against the roller with which it was itself embossed. Adhesive has previously been applied to the peak of the protuberances of the latter ply. The combination of this ply with the other one is carried out via a roller known as a marrying roller, which exerts pressure on the whole assembly allowing the two plies to be joined.
Some applications require production of sheets that comprise several combined, but not embossed plies for certain uses, such as, for example in the field of wiping.
A first known installation that enables the combination of plies is shown schematically in FIG. 1. The installation comprises a smooth roller 1A1 and knurling wheels 1M1 and 1M2. The pressure of the knurling wheels on the combined plies may be sufficient to mechanically bond them without adhesive, but the pressure exerted must be particularly high. In this case, the imprint of the knurling wheels inevitably remains; moreover, it cannot be spread homogeneously, generating an irregular “rendering”.
FIG. 2 schematically shows a conventional installation for manufacturing a product of tip-to-tip type where a first embossing group 2C1-2A1 (rubber (C)-steel (A) comprising protuberances) is positioned in order to cooperate with a second equivalent group 2C2-2A2. In order to manufacture the two plies without marking, it could be imagined to separate the two rubber rollers 2C1 and 2C2 from their associated respective rigid roller 2A1 and 2A2. This solution would thus make it possible to produce, on one and the same installation, “embossed tip-to-tip” or “smooth” plies. The change in format could be carried out without modifying the passage of the sheet; it would be sufficient to apply or not the rollers 2C1 and 2C2. To combine the two plies together, it remains to deposit the adhesive with the applicator group BTA and to bond the two plies by exerting a sufficient joining pressure between the two rollers 2A1 and 2A2. Unfortunately, this solution has the drawback of not preventing the marking of the sheet when it passes between the two rigid rollers 2A1 and 2A2.
FIG. 3 shows another solution that uses a single embossing group comprising a deformable roller made of an elastomer 3C1 and a rigid roller with protuberances (made of steel) 3A1 associated with a marrying roller 3M. The installation would make it possible to manufacture a sheet with an embossed or non-embossed ply, depending on whether the rubber roller 3C1 would be pressed against the steel roller 3A1 or not. However, as before, it is not possible to avoid marking during passage in the bonding zone. If the roller 3M is soft the multi-ply sheet is embossed, which is not the desired solution; if the roller is hard, it is not possible to avoid the marking caused by the protuberances of the roller 3A1.
FIG. 4 shows an installation for manufacturing a “nested” type product. The installation comprises two embossing groups 4C1-4A1 and 4C2-4A2. The two plies are embossed separately, respectively between the rollers 4C1-4A1 and 4C2-4A2, and then they are joined by means of a marrying roller 4M. By separating the two rollers 4C1 and 4C2 from their associated rigid roller, the two plies are not embossed. This arrangement therefore makes it possible, as in the preceding propositions, to manufacture one of the embossed or non-embossed plies. However, it is not possible to avoid marking the sheet when it passes between the marrying roller 4M and the associated steel roller 4A1, since the roller 4M inevitably presses the sheet against the protuberances of the roller 4A1 in order to bring about the joining of the plies.